Wiper systems for wiping moisture from vehicle windows are well known. A typical wiper system includes an oscillating motor that moves a wiper arm and attached wiper blade through a wiping arc of between about 90° and 180°. The wiping pattern produced by the blade is an arcuate area bounded on the ends by the extremes of blade travel and on the outer and inner edges by the radii of travel of the outer and inner tips of the wiper blade. It is a necessary consequence of a prior art oscillating system that window areas outside the wiping pattern are not wiped. Where the aspect ratio (defined herein as the height:width ratio of the surface to be wiped) is low, as in most current vehicle windshields, two such wiper systems may be required in tandem and having overlapping patterns. For extremely low aspect ratio windshields, as in some sports cars (for example, the E-type Jaguars), even three overlapping wiper systems are known.
On many current vehicles, such as hatchback and sport utility vehicles (SUVs), it is known to provide an oscillating wiper system for the rear windshield. The pivot location for the motor may be on the windshield itself or on the vehicle body; the pivot location may be at the top or the bottom of the windshield; and the pivot location may be anywhere to the left or right of center. All such known positions represent attempts by vehicle manufacturers to maximize the wiping effect of a single oscillating wiper system, or in other words, to minimize the geometric incompatability of an arcuate wiping pattern on a rectilinear window.
Prior art arcuate wiping patterns on vehicle rear windshields are annoying and dangerous to the operators of these and other vehicles. Whether by road spatter, vehicle exhaust, rain, or snow, during vehicle use under adverse road conditions the non-wiped areas rapidly become opaque and useless to a vehicle operator in seeing other vehicles to the rear or which may be attempting to pass. To keep non-wiped areas useful in such conditions, a vehicle operator must stop frequently and clean those non-wiped areas by hand; in practice, most drivers simply ignore those areas and drive with decreased rear-windshield visibility, at increased hazard to themselves, their passengers, and the occupants of other vehicles.
In the prior art, various approaches are known to increase the area of a windshield wiped by an oscillating wiper. See, for example, U.S. Pat. Nos. 4,732,048; 4,847,941; 4,991,252; 4,979,259; 5,093,953; 5,408,719. In these disclosures, various complex arrangements of gears, pistons, levers, and/or cams displace a wiper blade during its rotary oscillation such that a greater proportion of a windshield is wiped than would occur in a simple rotary oscillation. None of these inventions purports to sweep a fully rectangular area of a windshield, however.
U.S. Pat. No. 4,245,369 ('369) discloses an elegantly simple apparatus for using oscillating motion to drive a wiper blade in a straight line over a windshield surface, and for keeping the wiper blade in a vertical attitude during wiping. Thus, a true rectangular wiping pattern may be achieved. A wiper arm linkage oscillatingly driven by an attached motor about a fixed pivot point above the pivot end (“inner end”) of the wiper arm in the y-axis direction causes the wiper arm pivot to be displaced upwards or downwards along a track in precisely the proportion needed to cause the other end (“outer end”) of the wiper arm to track in a straight line across the windshield. A parallelogram linkage causes the associated wiper blade to remain vertical. This mechanism is discussed and shown in greater detail in the Detailed Description of the invention hereinbelow.
A drawback of this invention, however, is that it is useful over only relatively small angles of wiper arm oscillation. The example shown in the '369 patent is a 45° included angle (22½° half-angle), requiring a relatively short linkage and short displacement track, and resulting in a relatively narrow but truly rectangular wiping pattern. It will be seen, however, that as the included oscillation angle (“sweep angle”) is increased, the length of the wiper arm, the length of the linkage, and the length of the track must increase non-linearly in proportion to the tangent of the half-angle. Depending upon the size and shape of the windshield, the fixed pivot point may be geometrically required to be on the windshield itself when the included angle is still less than 90°, a practical impossibility. When the included angle is 120°, as is desirable for wiping of a low aspect ratio windshield, the fixed pivot point is centered on the linear tracking line of the free end of the wiper arm, a clearly impractical situation. Thus, this invention wherein a fixed pivot point is disposed above a vertical track is not applicable singly to wide windshields having relatively low aspect ratios requiring large included wiping angles. Indeed, the '369 patent teaches in its FIG. 1 to use two such wiping systems, side-by-side and having overlapping fields, to cover a low aspect ratio windshield.
What is needed in the art is a windshield wiping system for a low aspect ratio-windshield, and especially for a rear-windshield, that employs a linear-tracking single wiper arm assembly to wipe a rectangular pattern covering a very high percentage of the total windshield area.
What is further needed is such a system wherein the linear tracking motion is provided by mechanical transformation of the rotary motion of an oscillating motor, preferably a single motor.
It is a principal object of the present invention to wipe a large percentage of the surface area of a low aspect ratio windshield in a rectangular field by employing a single linear-tracking wiper mechanism.